Favstar gets even better if you sign in.
Tagging your music collection with correct information: apparently the hardest computer science problem today. NOBODY has a good solution.
If you were looking for a shining example of UI *and* UX polish in an iPhone app, look no further than IconFactory's Astronut. It's a gem.
Ok.. Spotify alone is amazing, but try Spotify + www.sharemyplaylists.com... holy shit!